This invention relates to methods for pressure bonding adhesive tapes to container ends.
Both pressure-sensitive and heat-activated adhesive tapes have been found useful in closure systems for containing beverages and drinks, e.g., see U.S. Pat. Nos. 3,389,827 (Brochman et al.), 3,990,603 (Brochman), 4,108,330 (Patterson) and 4,135,637 (Hannula). Pressure-sensitive adhesive tapes have generally been applied to container ends using apparatus comprising a vacuum wheel which cuts and applies predetermined lengths of tape to the container end. Non-heated elastomeric pads are then used to press and bond the lengths of pressure sensitive tape onto the container end, e.g., see U.S. Pat. Nos. 2,684,240 (Lindsey), 2,990,081 (DeNeui), 3,472,724 (Casey) and 3,750,511 (Toensing).
Heat activated adhesive tapes (i.e., adhesive tapes comprising thermoplastic adhesives) have generally been applied to preheated container ends using apparatus comprising a vacuum wheel or reciprocating pad and shear which cuts and applies predetermined lengths to the container end. Heated rigid and elastomeric bonding pads are then used to press the previously applied predetermined lengths of tape onto the container end at conditions of time, temperature, and pressure sufficient to cause the thermoplastic adhesive on the tape to melt and bond to the container end.
In many instances, it is advantageous to apply tapes to cover both the interior and exterior surface of the container end adjacent the preformed opening. In these cases, the bonding pads are shaped and are required to deform the tapes into the preformed opening and also to bond the adhesive of the interior tape to the adhesive surface of the exterior tape in the area of the preformed opening. These bonds must be made with minimum entrapment of air both between the tapes and also around the edge of the preformed opening.
Conventional bonding means such as those discussed above often are not suitable for bonding fragile adhesive tapes to container ends. In particular, such methods often result in tearing of fragile tapes when the tapes are deformed over the sharp steel edges circumscribing the preformed opening in the container ends since an excessive amount of force provided by a bonding pad is localized at those edges. Also, conventional bonding methods, as described above, often employ resilient, elastomeric bonding pads adjacent heated platens. Unfortunately, such pads are susceptible to wear and must be replaced frequently. Additionally, shaped elastomeric pads must be aligned very accurately with the preformed opening in the container end to function properly. This accurate alignment is often difficult to achieve and maintain in high speed equipment.